Plastic cards, which carry printed matter such as words, designs, pictures or other printed information on a plastic backing, are widely used for all means of commercial purposes, personal identification, visiting cards and the like. It would be highly desirable to print all such cards by means of laser printers, but this is not always possible in the present state of the art, for the following reasons.
Laser printing machines are known in the art and are widely used for a variety of purposes. Basically, the laser printing process comprises, as a first step, defining the subject matter to be printed in the form of an array of instructions that can be used to control the printing machine. A common way of doing this consists in scanning the subject matter to be printed and registering the results of the scanning in a processor's memory, in the form of an array of digital instructions. Said instructions control the emission of laser rays from a laser source. The laser beams impinge on a cylinder in a pattern controlled by the said instructions and electrostatically charge the surface of said metal cylinder at selectively predetermined spots. The selectively electrostatically charged cylinder passes in the vicinity of a reservoir of coloring matter in powder form. The coloring matter particles are attracted to the aforesaid selectively charged spots of said cylinder and form thereon a desired pattern. A print substrate is then passed into contact with the metal cylinder and the pattern formed by the color particles is deposited thereon. This operation is repeated for each color if a multicolor print is desired, usually four times to provide the basic colors magenta, cyan and yellow plus black, to produce a complete colored image. At this stage a colored image has been formed on the print substrate. In order to stabilize the image, the print substrate is passed between heated rollers, which fix or set the print so that it is permanent and stable.
However, the aforesaid process, while quite effective for a number of applications, cannot be satisfactorily applied for the production of cards which are made of materials sensitive to the combined application of pressure and heat, to which they are subjected in the setting section of laser printers. Hereinafter, these material will be generically referred to as "thermo-mechanically sensitive materials" or "thermo-mechanically sensitive (printing) substrates". Among such thermo-mechanically sensitive materials or printing substrates are synthetic printing sheets, which, when printed upon and set in conventional laser printers, become damaged to such an extent that they cannot be used at all. If an attempt is made to render the setting conditions of laser printers less severe, in order not to damage the plastic card backing, then the setting is insufficient, the print is not stable, and once again the card is not satisfactorily usable. An example of such synthetic printing sheets are those marketed under the trade mark Teslin.RTM. by PPG industries, Inc., Pittsburgh Pa. Teslin.RTM. is described as a single layer, highly filed, microporous plastic film, based on polyolefin material and containing about 60% by weight of silica, available in gauges ranging from 7 Mil up to 18 Mil. Its properties have been described by the manufacturer and are known to persons skilled in the art.
It is a purpose of this invention to overcome the difficulties met in laser printing thermo-mechanically sensitive materials, and to produce printed cards having a backing of said materials, which are fully satisfactory and of perfect quality.
It is another purpose to provide laser printed, multilayer cards which are mechanically extremely strong and cannot be separated mechanically, viz. without the application of solvents or heat into the layers of which they are composed.
It is a further purpose to provide such cards which can be printed, and if desired laser printed, on both sides.
It is a still further purpose to provide such multilayer cards that are made of highly pliable sheets and yet are relatively stiff and suitable for uses in which stiffness is a factor.
It is a still further purpose to provide such multilayer cards that are printed, if desired, over their entire area, without blank borders.
It is a still further purpose to provide a method for achieving all the preceding purposes and others that will appear as the description proceeds.
It is a still further purpose to provide an apparatus for achieving the aforesaid results, which apparatus is simple and not expensive to make, nor difficult to use.
Other purposes and advantages of the invention will appear as the description proceeds.